I can't test my applet programs in Firefox though it can run using appletviewer in cmd prompt or Netbeans IDE.
I think it's caused by Security reason because the class I'm testing uses "/images" folder from its current direction. When I test simple programs like HelloWorld.class, it's fine.
Hence, can someone advise how I can give assessment to use its subfolder to be displayed in browser/appletviewer ?
There may be more than one causes for the exceptions, but start with this one:
Caused by: java.io.FileNotFoundException: C:\Projects\HTP 6\WelcomeApplet\class.class (The system cannot find the path specified)
at java.io.FileInputStream.open(Native Method)
Applets can't use file I/O due to security reasons. To access files on the server you need to go a somewhat more complicated route. The http://faq.javaranch.com/java/CodeBarnApplets page has an example of how to do that; it's called HelloServerFile. It uses readers instead of the streams you're using, but you should have little problems rewriting it.